1. Field of the Invention
The present invention relates to a semiconductor device having a transistor and a rectifier.
2. Description of the Related Art
In recent years, a high electron mobility transistor (HEMT) using a gallium nitride (GaN)-based compound semiconductor has been used frequently. The GaN-based HEMT has a low resistance value and a high breakdown voltage, and accordingly, is frequently used for use in electric power, and specifically, for a power supply circuit.
By Kinzer (U.S. Pat. No. 7,498,617 B2), a HEMT is disclosed, which includes an antiparallel diode that prevents noise of an opposite polarity voltage by introducing a reverse current. The HEMT disclosed by Kinzer has an object to prevent damage and breakage of the HEMT, which result from the noise of the opposite polarity voltage, by adding the antiparallel diode.
The HEMT disclosed by Kinzer has heterojunction in which a first group III nitride semiconductor (GaN) and a second group III compound semiconductor (AlGaN) are stacked on a support body. The HEMT includes a first power supply electrode (source electrode) and a second power supply electrode (drain electrode), which are spaced apart from each other on the second group III compound semiconductor, and includes a gate structure between the first power supply electrode and the second power supply electrode. A diode (defined as a first diode) includes a cathode electrode allowed to also serve as the second power supply electrode (drain electrode) of the HEMT, and a Schottky electrode arranged apart from the cathode electrode on an opposite side with the gate structure. That is to say, a structure in which a function like a body diode is added to the HEMT is adopted. In the case of premising a GaN-based semiconductor device having a high-speed operation and a high withstand voltage, a high-speed operation is also required for the diode. Accordingly, a Schottky barrier diode using the Schottky electrode as an anode electrode is adopted for the first diode.
Moreover, Kinzer also discloses a HEMT to which a diode (defined as a second diode) having another structure than that described above is added. In a similar way to the first diode, the second diode includes a cathode electrode allowed to also serve as a second power supply electrode (drain electrode), and a Schottky electrode arranged between a cathode electrode and a gate structure. The second diode is a Schottky barrier diode in a similar way to the first diode.
However, in the first diode added to the former HEMT, though the cathode electrode is allowed to also serve as the second power supply electrode of the HEMT, the Schottky electrode (anode electrode) is arranged on another region than such a HEMT region. The first diode having such a structure has a current path independently of the HEMT. Therefore, the structure and performance of each of the HEMT and the first diode can be optimally set, and a degree of freedom in designing and fabricating the same is brought about. However, the region of the HEMT and the region of the first diode are required separately from each other, and accordingly, the former HEMT is inferior in area utilization efficiency of the semiconductor device.
Meanwhile, in the second diode added to the latter HEMT, the cathode electrode is allowed to also serve as the second power supply electrode, and the Schottky electrode is arranged on the region of the HEMT. Accordingly, the latter HEMT is superior in area utilization efficiency. However, a part of a current path of the HEMT is used as a current path of the second diode, and accordingly, it is difficult to achieve reduction of forward voltage of the second diode without deteriorating characteristics of the HEMT, and less flexibility in designing and fabricating the same is brought about.